The formation of ice on inlet surfaces of gas turbines reduces operating efficiency due to reduced airflow and causes possible blade damage due to ice being ingested when bleed-off air is directed to the iced surfaces.The problem of preventing turbine surface icing is that of initiating a flow of bleed- off air at the proper time to prevent icing as well as operating only for the period of time needed. The Holley ice detection system detects atmospheric conditions that lead to ice formation and initiates bleed-off air to warm inlet surfaces before ice formation. The Holley system operates on a sensor which includes both a humidity transducer and ambient temperature transducer mounted in a common housing. Bleed-off air is required only 25–30% of the time to prevent icing. The automatic system permits a marked reduction in labor requirements.